Business, science and entertainment applications depend upon computers to process and record data. In these applications, large volumes of data are often stored or transferred to nonvolatile storage media. This storage media may include magnetic discs, magnetic tape cartridges, optical disk cartridges, floppy diskettes, or floptical diskettes. Typically, magnetic tape is the most economical and convenient means of storing or archiving the data. Storage technology is continually pushed to increase storage capacity and storage reliability. Improvement in data storage densities in magnetic storage media, for example, has resulted from improved medium materials, improved error correction techniques, and decreased areal bit sizes. The data capacity of half-inch magnetic tape, for example, is currently measured in hundred of gigabytes on 512 or more data tracks.
The improvement in magnetic medium data storage capacity arises in part from improvements in the magnetic head assembly used for reading and writing data on the magnetic storage medium. A major improvement in transducer technology arrived with the magnetoresistive (MR) sensor originally developed by the IBM Corporation. The MR sensor transduces magnetic field changes in an MR stripe to resistance changes, which are processed to provide digital signals. Data storage density can be increased because a MR sensor offers signal levels higher than those available from conventional inductive read heads for a given read track width. Moreover, the MR sensor output signal depends only on the instantaneous magnetic field intensity in the storage medium and is independent of the magnetic field time-rate-of-change arising from relative sensor/medium velocity.
The quality of data stored on a magnetic tape may be increased by increasing the number of data tracks on the tape, which also decreases the distance between adjacent tracks and forces neighboring read/write heads closer together. More tracks are made possible by reducing feature sizes of the read and write elements, such as by using thin-film fabrication techniques and MR sensors. In operation the magnetic storage medium, such as tape or a magnetic disk surface, is passed over the magnetic read/write (R/W) head assembly for reading data therefrom and writing data thereto. In modern magnetic tape recorders adapted for computer data storage, read-while-write capacity with MR sensors is an essential feature for providing fully recoverable magnetically stored data. The interleaved R/W magnetic tape head with MR sensors allows increased track density on the tape medium while providing bi-directional read-while-write operation of the tape medium to give immediate read back verification of data just written onto the tape medium. A read-while-write head assembly includes, for each of one or more data tracks, a write element in-line with a read element, herein denominated a R/W track pair, wherein the gap of the read element is aligned with the gap of the write element, with the read element positioned downstream of the write element in the direction of medium motion. By continually reading just-recorded data, the quality of the recorded data is immediately verified while the original data is still available in temporary storage in the recording system. In the interleaved head, the R/W track-pairs are interleaved to form two-rows of alternating read and write elements. Alternate columns (track-pairs) are thereby disposed to read-after-write in alternate directions of tape medium motion. Tape heads suitable for reading and writing on high-density tapes require precise alignment of the track-pair elements in the head assembly.
FIG. 1 illustrates a head 100 which can also function as a read-while-write head. As shown, the head includes several R/W transducer pairs 102 in a “piggyback” configuration. Servo readers 104 are positioned on the outside of the array of R/W transducer pairs 102. The servo readers 104 follow servo tracks for the particular data “band” of the tape being read or written to. Thus, signals from the servo readers are used to keep the head aligned with the band. The tape may have a single data band, or many data bands, and each band may have one or more servo tracks.
When the head is constructed, layers are formed on a substrate 110 in generally the following order for the R/W transducer pairs 102: an electrically insulative layer 112, a first shield (S1) 114 formed directly on the insulative layer 112, a sensor 116 also known as a read transducer, a second shield (S2) 118, and first and second writer pole tips (P1, P2) 120, 122. Note also that the second shield 118 and first writer pole tip 120 may be merged into a single structure.
Tape heads are constantly contacting the tape media during reading, writing and locating. This continuous contact can degrade head performance, resulting in an increase in error rates. Degradation can be caused by a variety of mechanisms. One is head wear caused by motion of the magnetic recording tape. Repeated passes of the tape medium over the tape head surface may eventually wear away some of the surface, which can impair head performance. This can be a particular problem for thin-film magnetic heads where the thin-film layer structure is less wear resistant than the tape supporting head portions, possibly leading to an unacceptably short lifetime for the magnetic head assembly. Very hard wear-resistant layers such as diamond-like carbon or titanium-carbide on the air bearing surfaces of magnetic heads inhibit gap erosion. However, such layers must be very thin, being perhaps 20 nanometers thick to ensure close head-tape spacing. Because they must be so thin, they tend to wear off over time.
Another magnetic head performance degradation problem is due to pitting and clogging of the insulation layer positioned between the substrate and nearest shield. It is believed that charging of the tape running over the head coupled with biasing of the shields and/or substrate can create high electric fields between head and tape and in the insulating layer, and cause electrostatic attraction of debris and even breakdown. This in turn tends to fracture or otherwise damage the insulating layer, forming pits therein. The pits become regions for debris accumulation, which in turn causes a variety of problems including shorting across the insulating layer and lifting of the tape away from the transducers. Also, the irregular electric field distribution in the preferred wafer substrate material Al2O3—TiC, or “AlTiC”, has hot spots at TiC grain corners. One solution to this problem has been contemplated. Heads may be made out of alternative ceramic wafers. However, other wafer materials are found to be less desirable due to generally poorer wear, fabrication issues, and heat conduction characteristics.
Another idea has been to make the undercoat thicker to reduce the fields. However, this resulted in more pronounced, wear. A thinner undercoat would seem desirable, but is found to have little benefit due to high fields and faster clogging.
There is accordingly a clearly-felt need in the art for a read/write head assembly with improved reliability. These unresolved problems and deficiencies are clearly felt in the art and are solved by this invention in the manner described below.